Motors are used as motive powers of various apparatuses that include a movable device, such as optical instruments and consumer use electronic products. According to high performance and size reduction in optical instruments, consumer use electronic products and the like, size reduction and higher power are required on driving mechanisms. To reply such requirements, a small sized DC geared motor has been used, and the small sized motor is coupled to multiple-stage reduction gears to achieve the same level of torque as that of a large sized motor. For example, Patent Document 1 relating to a motor rotation reducing mechanism that transmits a rotating force of a reversible motor to a driven object discloses a technology for reducing an installation space through installing plurality of rotatably supported gear gearing each other and alternately transmits rotation to increase a reduction ratio toward a rotating center shaft. However, because a driving device including such rotation reducing mechanism applies plurality of reduction gears, it requires wide installation space for reduction gears, i.e. a large space is required for the motor installation. In addition, drawbacks including poor stopping accuracy caused by backlash because of plurality of reduction gears and loud operation noise of the reduction gears are pointed out.
To solve these drawbacks, a driving device using an oscillation motor such as an ultrasonic motor has been proposed. The oscillation motor is constituted with a vibrator for generating specific vibration and a driven power transmission member in frictional-contact with the vibrator, and the motion energy of the vibrator transmitted to the driven power transmission member is converted to the motive power of the driving mechanism. Patent Document 3 discloses a driving device for an optical system which uses an oscillation motor as a motive power of a focusing operation in a lens barrel. The oscillation motor disclosed in Patent Document 3 includes an output shaft that is rotatably supported by a base member arranged along the outer peripheral surface of the output shaft, wherein a vibrator having a motive power output portion and a press member for making the motive power output portion of the vibrator contact with the outer peripheral surface of the output shaft are mounted on the base member, and the press member makes the vibrator contact with the output shaft to transmit a motive power of the oscillation motor to the output shaft. Such oscillation motor described above can enhance torque without using a plurality of reduction gear when compared to the DC geared motor disclosed in Patent Document 1 or the like.
[Patent Document 1] Japanese Patent Laid-Open No. 2002-168308
[Patent Document 2] Japanese Patent Laid-Open No. 2006-158054
[Patent Document 3] Japanese Patent No. 4182588